So-called on-demand-type ink jet recording methods have developed rapidly in recent years, among which the so-called bubble jet method, in which ink is heated to boiling by a heater and the force created by the bursting of the bubbles is used to eject ink onto a recording medium, has gained particular favor due to its several advantages, mainly the simplicity of the recording head structure and the density with which a multiplicity of nozzles can be packed onto the recording head. Thus, for example, in a bubble jet recording apparatus, in order to increase the number of nozzles of the recording head it is enough simply to increase the number of nozzles of the recording head.
However, driving a multiplicity of nozzles simultaneously requires instantaneous delivery of large amounts of power, which leads to the occurrence of power voltage drops. Accordingly, steady driving of the nozzles requires an extremely large current.
Moreover, bubble jet recording requires heating the ink to the point of boiling using extremely short pulse power of a few milliseconds in duration, so a large current flows when the nozzles are driven, causing a voltage drop. As a result, when driving a multiplicity of nozzles simultaneously the drive energy for driving the recording head is apt to be inadequate, causing the nozzle drive to become unstable, in other words degrading the recording image.
In order to avoid this problem, the conventional solution is to divide the nozzles of the recording head into a plurality of blocks, turn the blocks into drive control units and drive the blocks separately.
However, if the total number of nozzles is very large then the number of nozzles included in one block increases, with the result that the same voltage drop problem arises as when the nozzles are driven individually.
By the same token, reducing the number of nozzles included within a block and increasing the number of blocks in order to reduce the number of nozzles driven simultaneously within the same block results in an increase in the time required to drive the blocks by an amount equivalent to the number of additional blocks, thus necessarily reducing the drive frequency.
One common and widely known method for solving the voltage drop problem is called “remote sensing”. The remote sensing method involves detecting the voltage at the circuit portion of the end that consumes power and feeding the detected voltage back to the power source constant voltage circuit so as to maintain the voltage at the power-consuming end portion.
However, the remote sensing method requires a high-speed feedback circuit in order to feed back such an extremely short pulse current. Moreover, where the wiring is long a phase lag arises, making it impossible to operate the high-speed feedback circuit with stability, causing the circuit operation to become unstable and creating oscillation.
A previous application by the applicant, Japanese Laid-Open Patent Application No. 10-181017, discloses a method of counting the number of nozzles to be driven simultaneously and determining the length of the drive voltage pulse according to the count. This method involves predicting the voltage drop to be incurred based on the number of nozzles to be driven simultaneously and correcting the drive pulse length by an amount equivalent to the predicted voltage drop so as to deliver a predetermined amount of power, making it possible to drive the recording head with stability and without excess voltage.
However, the method described above also suffers from a disadvantage, in that unevenness in the wiring resistances of the drive circuit of the recording head and of the heat-emitting element make it difficult to perfectly correct the drive pulse length.
Moreover, in the event that a large capacity condenser is provided on the power supply wiring, the voltage drop cannot be completely corrected because the voltage drop is affected not only by the instantaneous current consumption but also by the immediately preceding power consumption.
Thus, as described above, a variety of factors contributed to fluctuations in the power supply voltage, and ordinarily even with a voltage drop, in order to ensure sufficient power required to drive the nozzles, the pulse length must of necessity be set rather larger than would ordinarily be the case. As a result, an excessive load is applied to the heat-emitting element and the heat-emitting element is therefore heated excessively, thus shortening the working life of the heat-emitting element and degrading the quality of the recorded image as overheating reduces the ejection capacity of the nozzles.